A77 sensor spots after 3 months of use

I a few at f22 fairly visible sensor spots. I went to the shop and they said that this is not a guarantee case, given that it might be from "wrong use" of the A77. He suggested to get a sensor clean for 50 EUR. I was a bit dissappointed by this reaction, if Im honest, in particular on the wrong use thing... but never mind.

Do I have to do cleaning by a supplier for another 50 EUR or can I do this myself? Both, the blower and the A77 internal cleaning function havent removed the spots. Secondly, is there anything that I can do to reduce the risk of spots?